1. Field of the Invention
The present invention relates to a light control module and method thereof, and in particular to a light control module and method appropriate for an optical pointing device.
2. Description of the Related Art
A mouse is a commonly used input device. A wheel mouse processes a displacement signal, a button signal, and an interface signal and communicates with a computer via an interface using the mechanical structure of its wheel and a micro-controller chip. An optical mouse replaces the mechanical structure of the wheel mouse with a complementary metal oxide semiconductor (CMOS) photo sensor chip capable of optical navigation. The CMOS photo sensor senses a series of continuous images of an operating surface. The displacement of the optical mouse can be determined by processing the images.
Typically, an optical mouse requires an auxiliary light source, such as a Light Emitting Diode (LED), supplying sufficient brightness for CMOS photo sensor operation. The LED flashes each time the CMOS photo sensor captures an image. Therefore, the auxiliary light source must provide sufficient and continuous brightness when the CMOS photo sensor captures a series of continuous images of the operating surface.
In practice, the auxiliary light source operates in accordance with a capture frequency of the CMOS photo sensor, to reduce power consumption and extend life. Thus, the auxiliary light source turns on when the CMOS photo sensor captures an image and turns off when the CMOS photo sensor is idle. When the auxiliary light source operates in accordance with a very low frequency CMOS photo sensor, flickers generated thereby are apparent and may cause discomfort for a user.
FIG. 1a is a diagram of the conventional optical mouse 1. FIG. 1b is a diagram of the under side of the optical mouse 1 in FIG. 1a. As shown in FIG. 1b, the optical mouse 1 has a photo sensor area 2 on the under side thereof for placement on an operating surface, such as a desktop. The photo sensor determines a displacement of the optical mouse 1 on the operating surface. FIG. 2 is a diagram showing operation of the photo sensor area 2 of the conventional optical mouse 1. As shown in FIG. 2, the optical mouse 1 comprises a photo sensor 3 and a light emitting diode (LED) 4. When the optical mouse 1 is moved on the operating surface 6, the LED 4 emits a beam 5 which is reflected by the operating surface 6 to the photo sensor 3, thus improving brightness for the photo sensor 3.
Typically, the LED 4 operates in coordination with the photo sensor 3. Thus, the LED emits light each time the photo sensor 3 executes a capture operation. When the optical mouse 1 is in a normal mode, for example being moved, the photo sensor 3 and the LED 4 both operate at a high frequency of 1500 Hz. When the optical mouse is in a standby mode, however, for example, when idle for some duration, the photo sensor 3 operates at a capture frequency of 30 Hz to reduce power consumption. Accordingly, the LED 4 also operates at a light emitting frequency of 30 Hz.
Typically, flickers from a light source are imperceptible when the frequency of the light source is greater than 60 Hz. However, as described above, when the conventional optical mouse 1 is in the standby mode, the photo sensor operates at the capture frequency of 30 Hz, and the LED 4 operates at the light emitting frequency of 30 Hz accordingly. Therefore, flickers from the LED 4 are apparent and may cause discomfort for a user.